Unlocking Immunity: How Killer Cells Differ in Adults vs. Newborns
"Exploring the role of FcRy-deficient and CD57+ natural killer cells in cytomegalovirus immunity, and what it means for understanding immune development."
Our immune system is a complex network of cells and processes that protect us from a constant barrage of threats, from viruses to tumors. Natural killer (NK) cells are a critical part of this defense, acting as first responders to identify and eliminate infected or abnormal cells. Understanding how these cells function and vary across different populations and life stages is crucial for developing effective strategies to combat disease.
NK cells are equipped with a range of receptors that either activate or inhibit their function, allowing them to precisely target threats while sparing healthy tissue. These receptors respond to signals on other cells, determining whether an NK cell will attack or remain passive. One key player in this process is the FcRy protein, essential for transmitting activating signals in NK cells. However, some NK cells are deficient in FcRy (g¯NK cells), and these cells have been linked to prior exposure to cytomegalovirus (CMV), a common herpes virus.
In a CMV-endemic area like Korea, where a large percentage of the population has been exposed to CMV, it's important to understand the prevalence and characteristics of these g¯NK cells. This article explores a study comparing the frequency and properties of g¯NK cells and CD57+ NK cells (another marker associated with CMV infection) in adult blood versus cord blood from newborns, providing insights into how CMV shapes the NK cell landscape from birth.
NK Cells, CMV, and Immune Memory
Natural killer (NK) cells help control cytomegalovirus (CMV), while CMV has evolved multiple ways to evade NK-cell responses. This interaction can leave a lasting imprint on the wider immune system and affect responses to other pathogens and vaccines. Some NK-cell subsets, called adaptive or memory-like NK cells, show persistence and cytotoxicity associated with adaptive immune responses, even though NK cells are conventionally considered part of innate immunity. NK cells also help defend against infection without prior sensitization and recruit other immune cells through cytokines and chemokines.
Key Differences in Killer Cells: Adults vs. Newborns
A recent study published in the Annals of Laboratory Medicine investigated the differences in NK cells between adults and newborns in a CMV-endemic Korean population. The researchers focused on two specific aspects of NK cells: the presence of FcRy deficiency (g¯NK cells) and the expression of CD57, a marker often associated with chronic viral infections like CMV.
- FcRy-Deficient NK Cells (g¯NK cells): All CMV-seropositive adult blood samples contained g¯NK cells, with a median proportion of 35% within the CD3/CD56dim NK cell pool. In contrast, g¯NK cells were rare in cord blood samples from newborns.
- CD57+ NK Cells: CD57+ NK cells were detected in all adult blood samples tested, but not in any of the cord blood samples.
CMV Evasion and Limits of Protection
Human cytomegalovirus (HCMV) is a ubiquitous herpesvirus that has co-evolved with its host over millions of years. The virus systematically subverts immune defenses, including natural killer cell responses, complicating efforts to achieve effective protection. A 2022 editorial notes that protection against CMV might benefit from virus-specific T cells: combining antibodies with vaccines that elicit CD8+ T cells may improve both humoral and cellular immunity.
Adaptive NK Cells and Immune Coordination
NK cells can contribute to immune defense without prior sensitization and can activate and recruit both innate and adaptive immune cells by producing cytokines and chemokines. Adaptive NK cells are also a distinct subject of study in relation to their differentiation and distribution across tissues. Together, these points highlight both NK cells’ role in coordinating immune responses and the specialized biology of adaptive NK-cell subsets.
Implications for Immunity and Future Research
This research highlights the dynamic nature of the immune system and how it adapts to environmental challenges like viral infections. The presence of g¯NK cells and CD57+ NK cells in adults, but not newborns, underscores the impact of CMV exposure on the NK cell landscape. It shows that the immune system is not static at birth but it develops over time.
CMV and Immune Reconstitution After Transplant
A 2026 single-cell analysis reports that asymptomatic CMV viremia after hematopoietic stem cell transplantation (HSCT) shapes immune reconstitution. The study describes oligoclonal CMV-specific CD8+ T-cell responses alongside adaptive NK-cell responses. It also reports that donor CMV serostatus strongly influences the timing, maturation, and function of CMV-specific T cells and adaptive NK cells after HSCT.
Adaptive NK Biology and Research Directions
Research on CMV-induced changes in NK-cell subsets challenges a strict division between innate and adaptive immunity, suggesting that environmental influences can shape immune cells across the human immune system. A 2026 systematic review describes its scope as integrating updated clinical-trial data, mechanistic innovations, tissue-resident NK-cell biology, and clinical outcomes to map trends and forecast the future of NK-cell immunotherapy. HCMV remains an important focus because it can evade antiviral defenses and establish lifelong persistent infection while reshaping the immune response.
These findings also raise questions about the role of these specialized NK cell populations in controlling CMV infection and preventing disease. Further research is needed to understand the precise functions of g¯NK cells and CD57+ NK cells, and how they contribute to overall immunity.
Ultimately, a deeper understanding of NK cell development and function could pave the way for novel strategies to enhance immune responses to viral infections, develop targeted immunotherapies, and improve overall health outcomes across the lifespan. This study emphasizes the importance of understanding our immune system.